Differential regulation of adapter proteins Dok2 and Dok1 in platelets, leading to an association of Dok2 with integrin αIIbβ3

Abstract

Background: We previously demonstrated that Dok2 is rapidly phosphorylated on tyrosine residues in platelets in response to thrombin, the immunoreceptor tyrosine-based activation motif-coupled collagen receptor glycoprotein (GP) VI, and by integrin αIIbβ3. Objectives and methods: In this study we further delineate the regulation of phosphorylation of Dok2 and compare this to the related adapter Dok1. Results: We demonstrate expression of Dok1 in platelets and the unexpected observation that the adapter protein undergoes tyrosine phosphorylation in response to thrombin but not to GPVI or integrin αIIbβ3. Furthermore, Dok1 phosphorylation is transient, peaking at 30s and returning to basal by 5min, whereas Dok2 phosphorylation is delayed but sustained. Dok2 phosphorylation, but not that of Dok1, is inhibited by Src kinase inhibitors and by chelation of intracellular calcium. Further, phosphorylation of Dok2 by thrombin and integrin αIIbβ3 in mouse platelets is independent of Syk and phospholipase Cγ2. Additionally, Dok2 coimmunoprecipitates with integrin αIIb β3 downstream of Src kinases. Conclusions: These results demonstrate differential modes of regulation of Dok1 and Dok2 in platelets. Further, they raise the interesting possibility that Dok2 plays an important role in integrin outside-in signaling through a physical and functional interaction with integrin αIIbβ3. © 2007 International Society on Thrombosis and Haemostasis.